Positron Emission Tomography (PET) scans follow the movement of a radioactively labeled compound throughout the body and are often used to detect metabolic activity in cancer cells relative to normal cells. The labeled compound is most likely:

The correct answer is glucose.

Explanation:

A nuclear medicine functional imaging apparatus, which has an application in witnessing the metabolic procedures taking place within the body and also helps in the process of diagnosing conditions like cancer is known as PET or Positron Emission Tomography.  

In the process, trace amounts of radioactive substances known as radiopharmaceuticals or radiotracers, a specific camera, and a computer are used to assess the functions of organs and tissues within the body. In the given case, the labeled compound would most probably be glucose, as the process of glycolysis takes place at a greater rate within the body and thus glucose can travel all over the body.  

i think that it is plants